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in Journal of the American Veterinary Medical Association


The value of magnetic resonance imaging (MRI) for the evaluation of dogs with pituitary-dependent hyperadrenocorticism (pdh) and cns signs was assessed. Magnetic resonance imaging of the brain was performed in 13 dogs with pdh and neurologic signs. The diagnosis of pdh was made on the basis of results of adrenocortical function tests and abdominal ultrasonography, in conjunction with appropriate history, clinical signs, and clinicopathologic alterations. Eight dogs had been treated with the adrenocorticolytic agent, mitotane, for 1 to 30 months before the development of neurologic signs.

Prior to mri, each dog had progressive neurologic signs that could not be attributed to hypocortisolism or mitotane toxicosis. The neurologic signs most frequently detected were disorientation and ataxia. Mean age of dogs at the time neurologic signs developed was 9.5 years. Sex predilection was not detected; however, most were large-breed dogs, with 11 of the 13 dogs weighing more than 20 kg.

A large mass in the pituitary gland, suprasellar region, or both was easily identified on the magnetic resonance images of each dog. The masses ranged from 8 to 24 mm in size. Expansion of tumors into the suprasellar region and compression of structures adjacent to the pituitary gland were readily detected by MRI. Contrast enhancement did not improve tumor identification, but did enable better delineation between tumor and surrounding structures.

After the diagnosis of a macrotumor was made by MRI, radiotherapy was initiated in 9 dogs and was successfully completed in 6. Three dogs had a relapse of neurologic signs 8, 11, and 26 months after radiotherapy was completed. Three dogs are alive 8, 15, and 32 months after radiotherapy. Postmortem examinations performed on 7 dogs confirmed the diagnosis of pituitary macroadenomas. In 4 dogs, postmortem examination was performed within 1 month of MRI, providing a means to substantiate results. Magnetic resonance imaging provided accurate information on tumor size and the extent of tumor expansion into the surrounding structures.

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in Journal of the American Veterinary Medical Association


To evaluate magnetic resonance imaging (MRI) brain scans of dogs with pituitary-dependent hyperadrenocorticism (PDH) and no signs of CNS dysfunction 1 year after diagnosis and initial MRI.


Prospective study of surviving dogs from a previous study.


13 dogs underwent MRI of the brain at the time that PDH was diagnosed and prior to treatment. At that time, none of the dogs had clinical signs suggestive of an intracranial mass. Approximately 1 year after diagnosis and MRI, the brain was again evaluated by MRI.


On the initial MRI scan, 5 of the 13 dogs had normal findings, and 8 had evidence of a mass (tumor) in the area of the pituitary gland. Of the 5 dogs that had no visible pituitary mass on the initial MRI scan, 3 had a normal MRI brain scan 1 year later. Of the 5 dogs that had no visible pituitary mass on initial MRI scan, 2 had a visible pituitary mass at 1 year. The 8 dogs that had a visible mass on the initial MRI brain scan had easily identified pituitary masses on the second MRI scan. Of these 8 dogs, 4 had no apparent change in pituitary mass size, and 4 had obvious increase in vertical height of the pituitary mass. Of the 4 dogs, 2 developed signs of neurologic dysfunction within 1 year after diagnosis of PDH, presumably attributable to that mass. Of the 13 dogs, 12 were treated with mitotane soon after completion of the initial MRI scan. Sensitivity to mitotane and initial pituitary mass size or growth were not correlated. Of the 13 dogs evaluated initially and 1 year after diagnosis, 10 had pituitary masses identified on MRI brain scans.

Clinical Implications

The incidence of visible pituitary masses among dogs with PDH at the time of or within a year of diagnosis was > 75%. In 2 dogs, signs of CNS dysfunction developed within 1 year of PDH diagnosis when pituitary masses were ≥ 10 mm. (J Am Vet Med Assoc 1996;208: 1268–1273)

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in Journal of the American Veterinary Medical Association


Magnetic resonance imaging was used to determine the prevalence of visible pituitary masses in 21 dogs with recently diagnosed and untreated pituitary-dependent hyperadrenocorticism. All dogs had clinical signs and routine database values (CBC, serum biochemical panel, and urinalysis) consistent with a diagnosis of hyperadrenocorticism, and none had clinical signs suggestive of an intracranial mass. Each dog had plasma cortisol concentrations after adrenocorticotropic hormone administration or low-dose dexamethasone administration consistent with hyperadrenocorticism. Pituitary-dependent hyperadrenocorticism was confirmed by the finding of 2 equal-size adrenal glands on abdominal ultrasonography and by results of plasma endogenous adrenocorticotropic hormone concentration and high-dose dexamethasone suppression testing. Sagittal and transverse Tl-weighted magnetic resonance images of the brain were obtained before and after IV administration of gadopentenate dimeglumine.

Eleven dogs had visible masses, ranging in size from 4 to 12 mm at greatest vertical height. Mean age and body weight of dogs with a visible pituitary mass was not significantly different from dogs without a visible mass. There was no significant difference in endocrine test results when comparing dogs with a visible pituitary mass to dogs without. The prevalence of visible pituitary masses in dogs with pituitary-dependent hyperadrenocorticism was greater than suggested by the prevalence of clinical neurologic signs.

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in Journal of the American Veterinary Medical Association